1. Field of the Invention
This invention relates to control systems for plurality of stepper motors, and more specifically, stepper motor control systems for plural stepper motors wherein operating hardware and consequently cost of the control system is minimized.
2. Description of the Prior Art
Stepper motors are extensively used in a wide variety of equipment ranging from transport vehicles to manufacturing apparatus to printing apparatus. In the traditional and most straightforward operation of stepper motors, each motor has associated therewith a controller which determines the mode of operation of the stepper motor, i.e., the current characteristics to be provided to the windings of the stepper motor as well as the driving of the stepper motor which involves the sequence in which the plurality of windings in the stepper motor are energized by being respectively connected and disconnected to a current supply which provides the above-mentioned current of predetermined characteristic to the energized windings of the motor.
The art has recognized that with apparatus employing a plurality of stepper motors and particularly stepper motors which operate during operational cycles mutually exclusive of each other, if two or more of such stepper motors shared a single controller, then considerable savings could be achieved through the elimination of duplicate controllers. U.S. Pat. No. 4,055,786 discloses such a stepper motor control system wherein two or more stepper motors share a single controller system. While such a shared controller system for a plurality of stepper motors did provide some valuable savings, these applications where limited to stepper motors which operated in substantially the same mode, i.e., all of the plurality of the stepper motors have to operate in an open loop mode or all had to operate in a closed loop mode. Also, all of the stepper motors had to utilize energizing currents of substantially the same characteristics.
Thus, apparatus with shared controllers could not be used for the operation of stepper motors which operated in different modes or had significantly different energizing current characteristics.